Why the universe still glows from the Big Bang

Lyman Page is a professor of astronomy at Princeton and his principal area of research has for decades been the heat afterglow of the big bang. My first thought on opening the book was: “This will be just another academic jumping on the popular science bandwagon and short-changing the public with a pretty ordinary book.” Nothing could be further from the truth. This ranks alongside Steven Weinberg’s The First Three Minutes as one of the best books on cosmology I have ever read.

The most striking thing about the night sky is that it is mostly black. However, if instead of seeing visible light, your eyes could see a type of invisible light known as microwaves, the most striking thing about the night sky would be that it is white. The entire universe is glowing with the “afterglow” of the big bang fireball. How could it not be when the light of the fireball was bottled up in the universe and so literally had nowhere to go? Greatly cooled by the expansion of the universe in the 13.82bn years since the big bang, the “cosmic background radiation” now consists of low-energy radio waves, principally microwaves.

Imprinted on the cosmic background radiation is a “baby photo” of the universe when it was a mere 400,000 years old and matter from the cooling fireball was beginning the long process of clumping under gravity that would culminate in galaxies such as our own Milky Way. From that photo can be extracted the six numbers that define our universe, from its age of 13.82bn years to the fact that 70 per cent of cosmic mass-energy is in the form of mysterious “dark energy” whose repulsive gravity is speeding up cosmic expansion.

Cosmic background radiation, in short, has ushered in the age of precision cosmology, which explains perhaps why this book is principally about that phenomenon. The Little Book of Cosmology is a compact treasure-trove of cosmic insights to be read, mulled over, and read again.

The Little Book of Cosmology by Lyman Page (Princeton, £16.99)